A pressure regulating valve is used to adjust the pressure of a fluid that is being conveyed under pressure to an intended pressure that can be predetermined by means of adjusting a spring tension or electrically by means of supplying a voltage to an electromagnet. The fluid being provided by a pump is subjected to a reduced pressure, the pressure being reduced by way of a controllable valve body to the intended pressure, wherein, if the pressure is too high, fluid is discharged from the pump line and respectively redirected back to the pump.
Automobile applications relating to the engine or transmission require that electrically controllable pressure regulating valves always demonstrate the identical control behavior within a large temperature range. It can be problematic when adjusting small pressures in the case of pressure regulating valves that have small dimensions and a low magnetic force characteristic curve. In the case of low temperatures (e.g. −20° C.), long switching times occur as a result of the high oil viscosity. In the case of a low temperature inter alia, it is not even possible to set low pressures since the valve body is not activated by way of the magnet and the valve consequently remains open.
DE 10 2010 024 585 A1 describes a solenoid valve having a solenoid, an armature that is connected to a valve member, and an oil-filled valve chamber in which the armature is arranged. In order to ensure good adjusting dynamics, the armature is mounted in a moveable manner in the oil of the system, wherein, in order to reduce the oil viscosity, the solenoid heat generated by the electrical current causes the temperature of the oil in the valve chamber to rise.
A control unit for a solenoid valve is known from EP 0 006 843 B2. In order to increase the activation force, the electrical current being directed through the solenoid is increased for a short period of time by means of a particular electronic switching process.
DE 601 08 998 T2 describes a control system for controlling an electromagnetic valve that comprises a solenoid pair, an element that is arranged in a moveable manner in the chamber between the solenoids, a valve body and also resilient means that in the case of non-energized solenoids hold the moveable element in a central position. During an initialization phase, the influence of the viscosity is ascertained by way of analyzing the oscillating behavior in the case of this particular valve and the electrical current required to control the valve is determined. In addition, the oil temperature is subsequently determined.
DE 38 43 138 C2 discloses a method for controlling and detecting the movement of an armature of an electromagnetic switching element of a valve. The change with respect to time of the voltage or rather of the electrical current is detected for the purpose of recognizing the termination of the armature movement.
DE 10 2006 061 105 A1 discloses a specially constructed valve for a cam shaft adjuster. The electromagnet is electrically energized by means of switching the voltage supply on and off within a predetermined time interval.
DE 20 2005 018 018 U1 describes a brake system having a piston-cylinder unit. The piston-cylinder unit is used to build-up and reduce braking pressure, to achieve the ABS function and the anti-slip control. The movement of the brake pedal is detected and taken into consideration when electrically controlling the electromagnetically controllable valve. The rotational acceleration of the wheel is likewise taken into consideration for the purpose of reducing the pressure, for reducing the braking effect.
In the case of the switching arrangement for operating the solenoid valves in accordance with DE 40 24 496 A1, a first control member is provided for applying an activation voltage and a second control member is provided for applying a lower operating voltage. An electrical current sensing member is provided in the operating current circuit and said electrical current sensing member adjusts the magnitude of the operating voltage in dependence upon the ascertained operating current.
DE 195 33 131 A1 describes a method for controlling an electromagnetic consumer—a solenoid valve of a diesel injection pump. The control voltage of an end stage is regulated during the switch-on phase until a switch-on peak electrical current achieves a predetermined value. The holding current is subsequently reduced in repeating steps to a predetermined value. This value is held constant for a period of time—subsequently, the electrical current is increased in order to initiate a switch-off phase.
A method for ascertaining a viscosity characteristic variable of a motor oil, which is described in DE 10 2010 020 757 A1, uses the valve switching times as a measure for the viscosity of the medium that is to be switched.